Background and study aims:The usefulness of a new quick test for endoscopic diagnosis of adult-type hypolactasia was tested in duodenal biopsies.In this test,an endoscopic biopsy from the postbulbar duodenum is incubated with lactose on a test plate,and a color reaction develops within 20 min as a result of hydrolyzed lactose(a positive result) in patients with normolactasia,whereas no reaction(a negative result) develops in patients with severe hypolactasia.Patients and methods:Two postbulbar duodenal biopsies were taken from 80 prospectively enrolled adult outpatients with dyspepsia.The biopsies were used for the Quick Lactase Test(Biohit PLC,Helsinki,Finland) and in biochemical disaccharidase(lactase,sucrase,and maltase) assays.In addition,the C/T-13910 genotype was determined from DNA extracted from gastric antral biopsies using polymerase chain reaction sequencing in genomic analysis of adult-type hypolactasia.Results:Twenty-one of 22 patients(95% ;95% CI,87-100%) with biochemical lactase activity < 10 U/g protein,but none of the 58 patients with lactase activity of 10 U/g protein or more had a negative result in the Quick Lactase Test.Seven of the 80 patients(9% ;95% CI,3-15%) had a Quick Lactase Test result that indicated mild hypolactasia(a mild color reaction) .All patients with celiac disease(n = 6) had a negative Quick Lactase Test result.Nine of 74 patients(six patients with celiac disease were excluded) had a CC-13910 genotype in genomic testing,indicating adult-type hypolactasia.All of them had negative test results with the Quick Lactase Test.Twenty-six patients had a TT genotype,indicating normolactasia,and none of these patients had a negative test result in the Quick Lactase Test.Six of 39 patients(15% ;95% CI,4-27%) with a CT genotype had a negative result in the Quick Lactase Test.Conclusions:The Quick Lactase Test effectively identifies patients with severe duodenal hypolactasia.In comparison with CC(adult-type hypolactasia) and TT individuals(normolactasia) ,the sensitivity and specificity of the Quick Lactase Test result was 100%.In comparison with biochemical lactase assays,the sensitivity and specificity of a negative Quick Lactase Test for indicating hypolactasia(lactase activity < 10 U/g protein) were 95%(95% CI,87-100%) and 100%,respectively. Background and research aims: The usefulness of a new quick test for endoscopic diagnosis of adult-type hypolactasia was tested in duodenal biopsies. This test, an endoscopic biopsy from the postbulbar duodenum is incubated with lactose on a test plate, and a color reaction develops within 20 min as a result of hydrolyzed lactose (a positive result) in patients with normolactasia, without no reaction (a negative result) develops in patients with severe hypolactasia. Patients and methods: Two postbulbar duodenal biopsies were taken from 80 prospectively enrolled adult outpatients with dyspepsia. The biopsies were used for the Quick Lactase Test (Biohit PLC, Helsinki, Finland) and in biochemical disaccharidase (lactase, sucrase, and maltase) assays.In addition, the C / T-13910 genotype was determined from DNA extracted from gastric antral biopsies using polymerase chain reaction sequencing in genomic analysis of adult-type hypolactasia. Results: Twenty-one of 22 patients (95%; 95% CI, 87-100%) with biochemical lactase activity <10 U / g protein, but none of the 58 patients with lactase activity of 10 U / g protein or more had a negative result in the Quick Lactase Test. Sevent of the 80 patients (9%; 95% CI, 3 -15%) had a Quick Lactase Test result that indicates mild hypolactasia (a mild color reaction). All patients with celiac disease (n = 6) had a negative Quick Lactase Test result. Nine of 74 patients (six patients with celiac disease were excluded had had CC-13910 genotype in genomic testing, indicated adult-type hypolactasia. All of them had negative test results with the Quick Lactase Test. Twenty-six patients had a TT genotype, indicating normolactasia, and none of these patients had a negative test result in the Quick Lactase Test. Six of 39 patients (15%; 95% CI, 4-27%) with a CT genotype had a negative result in the Quick Lactase Test. Conclusions: The Quick Lactase Test effectively identifies patients with severe duodenal hypolactasia.In comparison with CC (adult-type hypolactasia) and TT individuals (nthe sensitivity and specificity of the Quick Lactase Test result was 100%. In comparison with biochemical lactase assays, the sensitivity and specificity of a negative Quick Lactase Test for indicating hypolactasia (lactase activity <10 U / g protein) were 95% (95% CI, 87-100%) and 100%, respectively.